A multi-million dollar duel on Wall Street over whether Herbalife is the next hit diet pill company — or just a pyramid scheme — has landed in Washington.

The fight is fueled by outspoken billionaires who are opening their wallets to consultants and well-connected lobbyists — making it a full-fledged inside the Beltway throw down.

Billionaire hedge fund manager Bill Ackman’s $1 billion bet that the nutritional supplement giant is destined to fall under the weight of its own business practices became public in late 2012.

But legendary billionaire activist Carl Icahn fired back, buying up nearly 16 percent of the company and publicly backing its CEO and business model.

Now their hired guns are pressuring lawmakers to weigh in, especially members of the Congressional Hispanic Caucus because Ackman has alleged that Hispanics and other low income minorities are disproportionately targeted by Herbalife. And they are fighting over whether the Federal Trade Commission should investigate claims of fraud and potential pyramid schemes.

The battle is just the most recent example of Wall Street hiring K Streeters when there are hundreds of millions on the line, and, just as important — egos.

“It’s not purely driven by the balance sheet considerations,” said Paul Equale, a Democratic operative with a background in financial services. “These are the kind of guys who would have a $10 million lawsuit for a $1 million house. The economic value is an overlay, but it’s not really the driver.”

Ackman and Icahn are hardly the first activist investors to use the D.C. stage. For instance, San Francisco billionaire Tom Steyer has launched an aggressive campaign against the Keystone XL Pipeline and hedge funds with a large stake in Freddie and Fannie Mae have also gotten in on the action.

But the showdown between Icahn and Ackman is notable because it is personal and long brewing— the pair had a previous investment dispute that ultimately was resolved after multiple years of contentious litigation. It got particularly nasty after an epic verbal spat on CNBC in January where the two faced off making waves in the financial world.

Since then Icahn has continued to stoke the messaging wars after Herbalife stock rebounded. The stock price has rallied as high as 90 percent above where it traded at the beginning of the year and is at its highest price since investors first started questioning its business practices.

“I like Ackman,” Icahn said during a recent speech. “Anybody that makes me a quarter billion dollars I like.”

Meanwhile, Ackman has focused inside-the-Beltway, urging the Federal Trade Commission to investigate the company and has argued that it takes advantage of low income and minority groups.

Ackman’s hedge fund estimates that more than 90 percent of the monetary benefits obtained by Herbalife distributors come from recruitments, not sales, according to a company report. Ackman and his hedge fund Pershing Square declined to comment.

Herbalife defends its business practices.

“Like many publicly-traded companies, Herbalife works with a range of consultants to help us navigate policy and regulatory issues impacting our business,” said Diane Turpin, Herbalife’s vice president of worldwide regulatory government and industry affairs said in a statement. “It’s no secret that our reputation is under assault by a billionaire hedge fund manager whose only interest is financial gain. We are proud of our 33-year track record of success, and have a responsibility to defend ourselves against a relentless, well-financed effort to discredit our business model.”

Turpin added the company remains focused on distributors, customers and employees — and shareholders.

Ackman said at an investor conference in December that he plans to donate any profits to charities.

“I view this as blood money,” Ackman said a the time.

Ackman and investors in his Pershing Square hedge fund have vocally bet against the company, shorting more than 20 million shares of Herbalife in December, betting roughly $1 billion that the company’s stock would decline in value.

The National Consumers League, the Hispanic Federation and Rep. Linda Sanchez (D-Calif.)have sent letters to the FTC asking for an investigation into Herbalife’s business practices. LULAC, NCL, U.S. PIRG and others recently met with the FTC to press their case in person.

Ackman’s Pershing Square also hired up K Street talent bringing on Moffett Group and Wexler & Walker Public Policy Associates at the end of May. He has also brought on Global Strategy Group’s Bill Burton to assist in messaging and strategy. Pershing Square spent $54,000 on lobbying in the second quarter, according to lobbying reports.

Those consultants have also been lobbying the Congressional Hispanic Caucus to weigh in with the FTC against Herbalife.

His surrogates have worked with Rep. Loretta Sanchez (D-Calif.), who is trying to line up lawmakers to sign onto a letter she is sending to the FTC. Her legislative director sent an email last week trying to set up a call with other CHC members with a representative from Ackman’s hedge fund. The call ended up getting canceled.

Moffett Group’s Amanda Thayer also has sent emails last week urging CHC staff to get their bosses to sign onto Sanchez’s letter.

“As members of Congress, we are particularly concerned about the welfare of our constituents, and about the American consumer,” the letter reads. “Many of us represent districts with significant numbers of ethnic and racial minorities, and, as such, we have found the allegations that Herbalife’s business and marketing practices unfairly and disproportionately target minority populations particularly troubling.”

Rep. Xavier Beccera (D-Calif.), meanwhile, weighed in with his colleagues last week arguing that they shouldn’t send a caucus-backed letter. Herbalife’s headquarters is located in Becerra’s district and the company has contributed heavily to his reelection efforts.

“It’s totally appropriate for Members of Congress to be vigilant in protecting the rights of their constituents and consumers,” Becerra said. “But to do that, we need to have the facts.”

Herbalife has also gotten involved hiring up lobbying firms the Podesta Group, Ogilvy Government Relations and the Raben Group to try and defend Herbalife on Capitol Hill. Herbalife already retained Downey McGrath. Glover Park Group is also working for the company on strategy and communications.

Since Ackman’s big push with the CHC, Ichan’s hired guns have been making the rounds to those offices to make their case and dispute Ackman’s case, according to sources familiar with the effort.